1. Field of the Invention
The present invention relates to a hybrid vehicle running in combination of traction of an engine (internal combustion) and traction of a motor (electric motor), particularly to a hybrid vehicle provided with a first transmission path that transmits engine traction to driving wheels and a second transmission path that transmits a motor traction to the driving wheels.
2. Description of the Related Art
Conventionally, it has been well-known that a hybrid vehicle runs by utilizing characteristics of each traction of an engine and a motor, in which a second transmission path that transmits the motor traction to the driving wheels is used when the vehicle speed is less than a given value (vehicle speed V1); a combination of a first transmission path that transmits the engine traction to the driving wheels and the second transmission is used when the vehicle speed is V1 or more; and the hybrid vehicle runs chiefly through the first transmission path transmitting the engine traction to the driving wheels when the vehicle speed reaches around the maximum speed Vmax. In such a hybrid vehicle, as disclosed in JPB2942533 (Paragraph [0015] to [0028], FIGS. 1, 2), for example, a gear ratio of the first transmission path is defined such that the characteristic of the engine traction covers the maximum speed Vmax, thereby to simplify a transmission system of the vehicle without providing a transmission mechanism which has a variable gear ratio for the first and second transmission paths. Accordingly, when the vehicle speed reaches around the maximum speed Vmax, the vehicle runs with the engine traction trough the first transmission path to the driving wheels.
However, according to such a hybrid vehicle disclosed in JPB2942533 (Paragraphs [0015] to [0028] and FIGS. 1, 2), in a steady running state with a smaller load (cruising), the vehicle is designed to run in a series driving mode in which the engine generates electric power, whereby the motor drives the driving wheels, or to run by using the first transmission path that includes a transmission device in which a reduction gear ratio is defined to be relatively greater (lower gear ratio) in order to achieve the maximum speed Vmax by using the engine traction.
However, there are such disadvantages: fuel efficiency of the vehicle may become lowered since transmission efficiency of the traction becomes relatively lowered; in addition, when running with the engine traction alone through the first transmission path including a transmission device in which a lower gear ratio is defined, the vehicle runs at the lower gear ratio to realize engine traction characteristics that achieves the maximum vehicle speed Vmax. Since the rotational rate of the engine significantly varies depending on the vehicle speed in a steady running state, it is difficult to select a region of the engine rotational rate that can provide higher fuel efficiency for the steady running state.
In particular, in a combination of an engine traction and a motor traction in a hybrid vehicle having a large displacement volume engine, such a large displacement volume engine has a greater excess traction, resulting in significant deterioration in fuel efficiency in the first transmission path including the transmission device in which a lower gear ratio is defined, as described above. In combination with this large displacement volume engine, even though the large displacement volume multi-cylinder engine is provided with an output characteristics variable mechanism for a variable displacement or the like in order to enhance fuel efficiency, it is difficult to make the most of this output characteristics variable mechanism performing a variable displacement for fuel efficiency enhancement at the lower gear ratio defined as described above.
JPB2942533 mentioned nothing about a driver's selection of a running condition by using a shift lever or the like; therefore, it is impossible to cope with a situation against the driver's will.
In the light of the above-mentioned disadvantages, it is desirable to provide a hybrid vehicle that enhances fuel efficiency of the vehicle as well as allowing a driver to select a running condition that meets his or her will.